It is becoming increasingly difficult, both in terms of cost and site availability, to construct conventional open reservoirs for the storage of water. Such reservoirs typically require the construction of a dam across a river, thereby flooding vast expanses of land upstream of the dam while severely curtailing the flow of water downstream from the dam. In light of the increasing value of water and the complexities of the various water laws across different jurisdictions, it is becoming prohibitively difficult to form an open reservoir in this manner.
In addition, open reservoirs have several disadvantages. One disadvantage is that they preempt any current or future use of the land other than to store water. That is, as additional land surface is devoted to the storage of water in open reservoirs, that same land surface is unavailable for alternative uses such as farming or open space.
A further disadvantage of storing water in open reservoirs is the high degree of evaporative losses experienced by such reservoirs due to the relatively large air/water interface. Specifically, in arid climates (such as those found in the Western United States), open reservoirs are subject to extremely large evaporative losses. Indeed, such evaporative losses are typically greatest where water is needed most.
A further unfortunate disadvantage to open reservoirs is that the reservoirs are highly susceptible to contamination. While previous contamination concerns have been limited to accidental chemical spills, petroleum leaks, polluted surface-water runoff, and the like, a more immediate threat is that of intentional contamination as part of a terrorist act.
Yet another disadvantage relates to detrimental temperature effects caused by surface water storage. For example, a surface water storage reservoir may contain water that is too warm to support indigenous species of fish and other animals. Discharge of the warm water from the reservoir could then damage the downstream fish populations.
Underground porosity reservoirs, such as those described in U.S. Pat. No. 6,840,710 to Peters et al., titled UNDERGROUND ALLUVIAL WATER STORAGE RESERVOIR AND METHOD, have been posited as an alternative to open reservoirs. Underground porosity reservoirs include a volume of porous material, such as natural alluvium, bounded by substantially impermeable walls to create an underground vessel capable of storing water. Underground reservoirs potentially can be used without the loss of surface use of the site. Underground reservoirs are also not subject to evaporation losses and are less susceptible to intentional and accidental contamination.
However, underground porosity water reservoirs also have drawbacks when used for water storage. First, typical water diversion techniques suitable for filling open reservoirs, such as direct pumping from a surface water body or the use of surface diversion ditches, reduce the potential benefits of underground reservoirs. The use of existing diversion ditches directly impacts surface uses near a reservoir site and therefore reduce one major benefit of underground reservoirs. Additionally, surface ditches, which are typically unlined because of cost, increase the passive loss of water due to evaporation and infiltration, thus reducing another major benefit of underground reservoirs. Furthermore, the diversion techniques mentioned above typically increase the sediment load in the water, which, as discussed below, is another factor that makes typical diversion techniques undesirable for use with underground reservoirs.
Second, unlike with open reservoirs, the sediment load of the water to be stored in an underground reservoir is very important. If water injected into an underground reservoir has a high sediment load, the alluvium surrounding the injection points may be clogged, reducing the effectiveness of the underground reservoir and reducing the storage capacity of the reservoir. Thus, care must be taken to monitor and maintain the physical quality of the water to be stored in an underground reservoir. Sediment control with open reservoirs, when performed at all, is typically achieved using a settling pond near the open reservoir. However, settling ponds represent a significant impact on surface use of the reservoir site and are undesirable for use in sites where impacts on surface uses are to be minimized.
Third, not all alluvium is chemically inert, and thus water injected into an underground reservoir may contain dissolved chemicals that react with the alluvium or porous material that provides the porosity of the underground reservoir. For example, a basic alluvium (e.g., an alluvium high in calcium carbonate) will chemically react with water that is acidic. This reaction could cause a precipitate to form that fouls the underground reservoir or changes the character of the water thereby rendering the stored water useless for its intended purpose.
In order to cost-effectively operate an underground porosity reservoir and minimize impacts to the surface uses, new methods of operation and management are required. The present invention provides a solution to these and other problems, and offers other advantages over the prior art.